In order to trap dust and other particulate matter contained in automobile exhaust gas and incineration exhaust gas generated upon incineration of waste products, a ceramic honeycomb filter is used. In particular, in order to efficiently remove particulate matter (hereinafter referred from time to time as “PM”) such as soot disposed from an internal combustion engine, a diesel particulate filter (hereinafter referred from time to time as “DPF”).
Since the DPF is finally clogged if trapped PM is not removed, it is necessary to remove the trapped PM for regeneration. The regeneration of the DPF can be performed generally by heating the DPF itself to combust PM. As a method for regenerating a DPF, for example, there is a method where an oxidation type catalyst is loaded to effectively combust PM by high temperature exhaust gas from a diesel engine.
When a catalyst is loaded on the DPF, the catalyst is generally loaded on the whole partition walls. By loading the catalyst on the whole partition wall, PM can effectively be combusted over the whole DPF. However, since temperature rises from an end portion (inlet side end portion) where exhaust gas flows in the DPF toward the end portion (outlet side end portion) where the exhaust gas flows out from the DPF, there arises a problem of catalyst deterioration in the vicinity of the outlet side endportion, crack generation in the partition wall, or melting of the partition wall when temperature in the vicinity of outlet side end portion of the DPF excessively rises.
To cope with this, there is disclosed a method to solve a problem of catalyst deterioration in the vicinity of the outlet side end portions of the DPF or the like by reducing the amount of the catalyst to be loaded or by loading no catalyst (see, e.g., Patent Document 1).
In addition, there arose a problem of insufficient regeneration efficiency in the case of repeated regeneration, there is disclosed a honeycomb filter capable of suppressing catalyst deterioration, crack regeneration of the partition wall, and melting of the partition wall and capable of enhancing regeneration efficiency upon regeneration (see, e.g., Patent Document 2).    Patent Document 1: JP-A-2003-154223    Patent Document 2: JP-A-2007-216165